The main objective of the proposed research is to assess the potential for using oxidants produced during the corrosion of granular and nanoparticulate zero-valent iron (ZVI) by oxygen to remediate contaminated groundwater and soil. This objective will be realized by studying the reaction mechanisms involved in oxidant production and contaminant transformation and the efficiency of potential treatment methods under conditions similar to those that are likely to be employed in treatment systems. The overall hypothesis that we aim to test is that the oxidative ZVI system offers a practical, cost-effective means of remediating contaminants that have the greatest impact on human health at Superfund sites. Our investigation of the reaction mechanisms will focus on the role of solution chemistry and surface structure on the rate of contaminant transformation. To gain insight into the processes occurring on or near ZVI surfaces, chemical processes occurring in the solution phase will be measured in conjunction with studies conducted using techniques designed to probe the surface, such as potentiometry, surfaceenhanced Raman spectroscopy and electrochemical quartz microbalance methods. Our investigation of the potential applications of the oxidative ZVI system to contaminant remediation will focus on permeable reactive barriers and water infiltration systems used to treat organic contaminants and drinking water treatment systems used to remove arsenic. These studies will extend the research in oxidant formation mechanisms to account for the effect of oxide coatings on the ZVI surfaces on contaminant oxidation rates and transport of contaminants to and from the corroding iron surfaces. This research has the potential to provide innovative and cost-effective ways of removing contaminants from groundwater and drinking water that are difficult or expensive to treat by conventional methods. The development of these technologies could reduce human exposure to organic and inorganic contaminants of concern.